Impact of gaps and sampling on the cross correlation. Upper panel: realistic light curve (black circles) with irregular sampling and seasonal observing gaps, generated based on the fiducial “continuous” light curve (light solid grey). Bottom panel: DCF obtained for the fiducial “continuous” light curve (black band), when data are obtained with a mean sampling of 1 point every three days (green band), when data are obtained with seasonal gaps of 130 days (blue band), and with a sparse sampling and seasonal gaps as shown on the upper panel (red points with error bars).